So many things could be making your scalp itch, its kind of hard to know where to start.
But, could be that you're having an allergic reaction or your scalp is dry as those are usually two of the more common issues. I get kinda itchy when I'm going through growth spurts as well so dunno, could be that too.
What does your scalp look like? is it scaly, do you see small white flakes? that can be caused by extreme dryness which a moisterizer could probably help with.
If you have like thick yellow stuff, then that would need a trip to the dermatologist.
When I was trying stuff during a pretty intense experimental phase I would sometimes get a really funky rash on my scalp..that was just an allergic reaction but at the same time it itched like MAD!
Instead of washing with shampoo, maybe you should try a cowash instead? If your scalp is dry it may be extremly beneficial. Plus it gives you a break from using shampoo which can also be drying too.
If you use hairsprays or gels, maybe its time to give them a break. Some topicals (sulfer seems to be a culprit) can make people have some scalp problems too, as can some types of shampoos. I limit SLS products to only around relax time (no help for it unfortunately) because I can have not so nice reactions to products containing it.
Try ruling out certain things to see if maybe something your using topically could be the cause. If you're not getting relief though you may need to just see a dermatologist.
HTH
-A
Also if you itch, maybe a scalp massage can also help.